1. It's not one of the reasons he gives in his official statement

And he's been through worse in the Senate than that, I wager:

ďI have been thinking hard about the decision whether to run for a sixth term in the United States Senate for a number of months - even more these last few weeks. Iíve reached a decision, and what Iíve decided really boils down to two things,Ē said Harkin. ďFirst, Iím going to fulfill a promise that I made to my wife Ruth, and that I also made to myself. It's a promise that weíre going to do certain things together - and that weíre going to live together in a way weíve often talked about - before it gets too late. Thatís a decision I believe many Iowans can relate to, either because of their own circumstances, or perhaps those of their parents. I have the privilege to be able to make this decision on my own terms, which not everyone can, and Iím deeply grateful to the people of Iowa that I do have that opportunity. Iíve been extremely fortunate. I was born here in Cumming in modest circumstances. My father was a coal-miner with just an 8th-grade education. My mother arrived to this country as an immigrant with virtually no earthly possessions. This state and this country have allowed me to enjoy a life and career beyond anything I imagined as a boy or young man.

ďSecond, I'm 73 years old right now. At the end of this term Iíll be 75. When the current Congress is over, I will have served in the United States House of Representatives and the U.S. Senate for a total of 40 years. After 40 years, I just feel itís somebody elseís turn. I canít put into words what an honor it is to serve Iowa. And I donít by any means plan to retire completely from public life at the end of this Congress. But I am going to make way for someone new in this Senate seat. I think that is right not just for me, but for Iowa, as well.Ē

3. I wouldn't expect him to put that in his official statement,

but I do believe it must have factored into his decision. I know that as I have gotten older, I find it more difficult to tolerate time consuming bullshit and disingenuous blather. With Reid's cave on the filibuster rule change, there will continue to be lots of time consuming bullshit and disingenuous blather in the Senate with few results. I don't blame Senator Harkin for deciding not to participate in this exercise in futility.

All the best to Senator Harkin. I hope he has a long and happy retirement.

4. I would expect him to put it in the statement, for two reasons

(1) He's one of the most straight-talking, unabashed members of the Senate, and he's never shied away from stating his strong opinions in the past
(2) Other senators who have retired over the past few years, who are far less outspoken than Senator Harkin, have cited the dysfunction of the Senate as reasons for their retirement.

7. He is a better man for that to be the reason for retiring.

Any blame for the filibuster belongs on the heads of the 7 Democrats that would not support the Udall/Merkley/Harkin reform.

It doesn't do any good to have a vote if it will be defeated. Even with the purpose of all of them on the record. That dooms the alternative because then the Republicans don't see the major reform as a threat when it goes down.